This invention relates to the means required to derive signals from magnetic recording media. More specifically, in magnetic disc devices where multiple heads are used on a single head arm and where selection of the single magnetic head is necessary to select a single region of the magnetic disc, this invention relates to a matrix amplifier device suitable for use with low impedance heads associated with high frequency recovery of magnetically recorded data.
In particular, one direction of development in the magnetic disc recording art relates to the use of low impedance one turn or a small number of magnetic pick-up and write heads which may be deposited on an appropriate magnetic medium, for example. Such one turn pick-up heads have the low impedance characteristics necessary for high rates of recovery of recorded magnetic data. In the prior art, magnetic heads typically consisted of many turns of a fine wire on an appropriate magnetic core. Such heads, consisting of many turns, have a comparatively higher impedance than a single turn head. Such prior art higher impedance heads were used in situations where multiple heads were associated on a single head arm assembly and a particular head of several was selected through use of a diode matrix arrangement to select a given region of the magnetic disc from which it was desired to recover data or write data. However, diodes have a comparatively high impedance and were suitable only for the several turn heads which also had a comparatively higher impedance. Diodes having a comparatively high impedance do not work effectively in a matrix selection arrangement with low impedance, one turn heads where the head impedance is considerably smaller than the impedance of the diode selection matrix.
Therefore, development of the high frequency one turn head is dependent upon the development of suitable low impedance matrix selection circuitry so that such heads may be used on a single head arm assembly. Similarly, the single turn heads have a comparatively low output which may be used advantageously with an amplifier circuit associated with the head arm assembly so that the output from the head arm assembly into the remainder of the apparatus will have a sufficiently high level amplitude so as to be uneffected by ambient electrical noise.